Use of a fertilizer containing l-amino acid for improving root growth and growth of mycorrhiza

ABSTRACT

The present invention provides a method of using a fertilizer, comprising an amino acid selected from the group of L-glutamine, L-asparagine and L-arginine as major nitrogen source, optionally together with inorganic nitrogen and/or a suitable preservative, for stimulating root growth, inducing more fine roots, increase the number of root tips and/or for stimulating mycorrhiza development.

The present invention relates to the use of a fertilizer affecting plantbiomass allocation. More specifically, the fertilizer is able tostimulate root growth, fine root development, increase the number ofroot tips and mycorrhiza development. Thus, the invention providesmethods for using the fertilizer in order to stimulate root growth, fineroot development, increase the number of root tips and mycorrhizadevelopment. Furthermore, the invention provides a method for using thefertilizer for modulation of the root fraction of the biomass.

TECHNICAL BACKGROUND

Allocation of growth between shoots and roots is a major process bywhich plant acclimates to various environmental conditions. It iswell-known that nitrogen supply is a major determinant of this process.At high nitrogen supply, growth of above ground parts is stimulatedrelative to that of structures below ground, while at low nitrogensupply, root growth is enhanced (FIG. 1). This strong dependence ofallocation on nitrogen supply has been demonstrated for a number ofplant species and for a range of different nitrogen addition rates.Nitrogen supply will, therefore, alter the structure of plants andhence, plant resistance to various stresses such as wind and drought.

The general idea of nitrogen effects on plant biomass allocation is thatat higher rates of N supply, plants sense a decreased need for nitrogenuptake and hence for root growth but an increase need for carbon uptakeand hence for shoot growth. This simple relationship between nitrogenand carbon access and biomass allocation may be regulated throughexternal cues and through sensing the levels of critical metabolitessuch as sucrose and glutamine within the plant.

During plant cultivation, ample supply of nutrients and in particular ofnitrogen is a prerequisite for good growth. As described above, highamounts of nutrients generally stimulate growth of above ground partsmore than of belowground parts and thus commercially cultivated plants,because of ample supply of nutrients; have often a high and unbalancedshoot mass fraction. There are, however, a number of situations in whichplants with a high root mass fraction are superior to those with a lowroot mass fraction. Typically, plants precultivated for plantationoutdoors or plants raised from cuttings should have a high root massfraction to enable efficient establishment following plantation. Thus,in all situations where plants or seedlings are precultivated for laterplantation, a high root mass fraction will be a positive factor forgrowth and establishment.

From what is described above it can be concluded that efficientcultivation of plants is incompatible with an optimal plant allocationpattern. The need for high growth rates during cultivation can only beachieved through application of high amounts of N which in turnstimulates shoot growth more than root growth and thus leads to animbalanced allocation. Ideally, plant cultivation conditions shouldallow for efficient growth but still have a high root mass fraction.With current cultivation methods, this cannot be achieved.

During the last decade, a number of studies have shown that organicnitrogen compounds and in particular amino acids are important nitrogensources for plants. These studies have demonstrated the occurrence ofamino acid uptake in both field and laboratory settings and for a rangeof different plant species, including mycorrhizal and non-mycorrhizalplants and also for a number of crop plants, e.g. wheat, corn, barley(Lipson and Näsholm 2001). Several studies have demonstrated howabsorbed organic nitrogen compounds are metabolized following rootuptake and also shown how nitrogen from such sources is incorporatedinto proteins. Moreover, a number of studies have demonstrated thatplants may use organic nitrogen compounds for growth. Thus, it is nowwidely accepted that organic nitrogen compounds such as amino acid mayfunction as nitrogen sources for plants.

It is generally held that all nitrogen forms following absorption (i.e.both inorganic and organic nitrogen forms) are metabolized and thusforms a common nitrogen pool within the plant, which is available forplant growth. Thus, according to this general knowledge, all nitrogenforms absorbed by a plant root would be part of a common nitrogen pooland therefore all forms of nitrogen absorbed by a plant root should bespread evenly within the plant.

It is known from in vitro studies in RU2016510 that protein hydrolysatecontaining a mix of amino acids have been used for stimulating rootingof callus and plant growth in hydroponic processes. Nothing is taughtabout the use of a pure natural L-amino acid for stimulating root growthof plants in this patent.

AU659115 discloses a process to manufacture and the use of a fertilizercontaining natural occurring L-amino acids, which are produced byenzymatic digestion of at least two proteolytic enzymes. AU659115 onlydiscuss the advantage of using small molecules (amino acids) asnutrients to enhance the up take. Nothing is taught about the use of apure natural L-amino acid for stimulating root growth of plants.Furthermore, nothing is taught about the simultaneously development ofmycorrhiza at the same time as it stimulates growth of the whole plantin these two patents.

EP 1,284,945 describes a fertilizer suitable for plants in particularconiferous trees. An advantageous feature of the fertilizer is that itis substantially stationary thereby minimizing undesirable nitrogenleakage to the environment. The main nitrogen source of the fertilizeris the L-form of a basic amino acid or its salt, in particularL-arginine. This document is completely silent regarding stimulation ofroot growth and mycorrhiza development.

Thus, there is still a need for a nitrogen-containing fertilizer havingthe ability of stimulating root growth and/or mycorrhiza development atthe same time as it stimulates growth of the entire plant.

It has been observed that plant of different species grow slowly or haveslow start when planted outdoors in forest regeneration.

It has further been speculated that a high root mass fraction and a highnumber of root tips or fine roots would help these small plants toefficiently establish in the new growth environment

In summary there is a need of a fertilizer that can be used to increasethe root mass fraction, the number of roots, root tips and the number offine roots on plants but without compromising growth of the whole plant.

SUMMARY OF THE INVENTION

It has now surprisingly been shown that it is possible to provide afertilizer capable of inducing and stimulating root growth as well asdevelopment of mycorrhiza at the same time as it stimulates growth ofthe whole plant.

The present invention provides a method of using a fertilizercharacterized in that it comprises a naturally occurring L-amino acid asnitrogen source for stimulating root growth.

Further this invention provides a method of using a fertilizercharacterized in that it comprises a naturally occurring L-amino acid asa nitrogen source for stimulating mycorrhiza development.

The present invention provides further a method of using a fertilizer,which comprises an amino acid selected from the group of L-glutamine,L-asparagine and L-arginine as major nitrogen source, optionallytogether with a suitable preservative, for stimulating root growthand/or for stimulating mycorrhiza development.

Further, it is disclosed the use of a fertilizer comprising a naturallyoccurring L-amino acid as a major nitrogen source for stimulating rootgrowth and/or for stimulating mycorrhiza development.

Further, it is disclosed the use of a fertilizer comprising a naturallyoccurring L-amino acid, in particular chosen from the group ofL-arginine, L-asparagine and L-glutamine as a nitrogen source, forstimulating root growth and/or for stimulating mycorrhiza development.

Further, it is disclosed the use of a fertilizer wherein in that thefertiliser also comprises inorganic nitrogen.

Further, the L-amino acid is chosen from the group of L-arginine,L-asparagine, glycine, L-glutamic acid and L-glutamine.

Further, it is disclosed the use of a fertilizer wherein at least 30%(wt) of the nitrogen source therein, preferably at least 70% (wt) of thenitrogen source therein, preferably at least 85% (wt), and mostpreferably at least 90% (wt), is a L-amino acid and the other nitrogensource is an inorganic nitrogen compound, such that the stimulation ofthe root and shoot growth is related to the ratio between the L-aminoacid and the inorganic nitrogen compound. In some examples the L-aminoacid is L-arginine and/or L-glutamine.

It is also disclosed a method for using the fertilizer for modulation ofthe root fraction of the biomass.

Furthermore, it is disclosed that the higher fraction of the nitrogensource that is a L-amino acid, the higher the root fraction is of thebiomass, i.e. more L-amino acid in the used fertilizer will give moreroots, more fine roots and many more root tips that can help the plantswhen planted outdoors.

Further, it is disclosed the use of a fertilizer comprising a naturallyoccurring L-amino acid wherein the fertilizer also contains a suitablepreservative.

Further, it is disclosed the use of a fertilizer comprising a naturallyoccurring L-amino acid wherein the preservative is selected from thegroup of a preservatives such as benzoic acid, acetic acid, salicylicacid, propionic acid, sorbic acid, citric acid, or their salts andalexin plus.

Further, it is disclosed the use of a fertilizer comprising a naturallyoccurring L-amino acid wherein the fertilizer is solid or is a solution.

The present invention also provides a method of using a fertilizer,comprising an amino acid selected from the group of L-glutamine,L-asparagine and L-arginine as major nitrogen source, optionallytogether with a suitable preservative, for stimulating root growth.

The present invention also provides a fertilizer comprising a naturallyoccurring amino acid. The naturally occurring amino acids that can beused in the fertilizer of the present invention are glycine, L-alanine,L-valine, L-leucine, L-isoleucine, L-serine, L-cysteine, L-threonine,L-methionine, proline, L-aspatic acid, L-asparagine, L-glutamic acid,L-glutamine, L-lysine, L-arginine, L-histidine, L-phenylalanine,L-tyrosine and L-tryptophan. In a preferred embodiment, the amino acidis chosen from the group of glycine, L-glutamic acid, L-glutamine andL-agrinine. Most preferably, the amino acid is chosen from the group ofL-arginine and L-glutamine as major nitrogen source. The fertilizer alsocontains a suitable preservative.

Preferably at least 30% (wt) of the nitrogen source therein, preferablyat least 70% (wt), preferably at least 85% (wt), and most preferably atleast 90% (wt), is a natural amino acid, such as L-arginine and/orL-glutamine.

Further, the use of a fertilizer could be characterized in that thefertiliser also comprises an inorganic nitrogen compound such as nitrateor ammonium for simultaneously stimulating root and shoot growth.

Further, examples of inorganic nitrogen compounds are nitrate, andammonium.

Preferably, the preservative is selected from the group of a benzoatesuch as potassium benzoate, acetic acid, salicylic acid, propionic acid,sorbic acid, citric acid, and alexin plus. A typical concentration ofpotassium benzoate amounts to 400-3000 ppm, preferably 600-2000 ppm andmost preferably 800-1200 ppm. A typical concentration of acetic acidamounts to 2000-10000 ppm, preferably 4000-8000 ppm, and most preferably5000-7000 ppm. A typical concentration of salicylic acid amounts to250-2000 ppm, preferably 500-1500 ppm, and most preferably 800-1200 ppm.A typical concentration of propionic acid amounts to 2000-10000 ppm,preferably 4000-8000 ppm, and most preferably 5000-7000 ppm. A typicalconcentration of sorbic acid amounts to 2500-20000 ppm, preferably5000-15000 ppm, and most preferably 7500-12500 ppm. A typicalconcentration of Alexin plus (Citrox Ltd, United Kingdom) amounts to10000-50000 ppm, preferably 20000-40000 ppm, and most preferably25000-35000 ppm.

Preferably, the fertilizer contains an additional component selectedfrom the group of magnesium sulphate, potassium sulphate, potassiumdihydrogen phosphate, potassium chloride, and trace elements, whereinthe trace elements are selected from the group of Fe, Mn, Cu, Zn, B andMo. Typically, the fertilizer may comprise 2-5% (wt), preferably 3-4%(wt) magnesium sulphate, 1-3% (wt), preferably 2-3% (wt) potassiumsulphate, preferably 4-5% (wt) potassium dihydrogenphosphate, 2-5% (wt),preferably 3-4% (wt) potassium chloride. Preferably, the trace elementsare added as a special trace element composition. An example of such acomposition is Micro+, available from LMI AB, Sweden. Typically, theamount of Micro+in the fertilizer is 4-5% (wt).

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be further described with reference tothe enclosed figures, in which:

FIG. 1 shows the effect of plant nitrogen status (% of N concentrationoptimal for growth) on plant biomass allocation expressed as fraction ofshoot biomass of total biomass. A, B and C refers to data fromexperiments with Picea abies, Pinus contorta and Pinus sylvestrisrespectively (from Ingestad & Agren 1986);

FIG. 2 reveals the content of nitrogen derived from uptake ofL-Glutamine and nitrate found in the whole plant and in the roots ofseedlings of Arabidopsis thaliana. The graph shows that absorbedL-Glutamine is preferentially used for root growth.

FIG. 3 discloses allocation of nitrogen derived from uptake ofL-arginine. Plants grown on 3 mM nitrate were supplied with smallamounts (30 μM) of N-15 labelled L-Arginine. Following 21 days ofcultivation, plants were harvested, roots and shoots were separated andsubsequently analysed for their content of N-15. The amount of N-15,expressed as atom % excess, in the two plant parts shows that nitrogenfrom L-Arginine is preferentially used for root growth;

FIGS. 4A and 4B shows biomass of Arabidopsis thaliana plants andallocation of biomass to roots and shoots of plants cultivated either onammoniumnitrate or L-Glutamine and nitrate (4A) and the root massfraction of plant cultivated either on ammonium nitrate or L-Glutamineand nitrate (4B);

FIGS. 5A and 5B reveals biomass of Populus plants and allocation ofbiomass to roots and shoots of plants cultivated either onammoniumnitrate or L-Glutamine and nitrate (5A) and the root massfraction of plant cultivated either on ammonium nitrate or L-Glutamineand nitrate (5B).

FIG. 6 discloses the chitin content of Scots pine roots. Plants wereeither cultivated with a mixture of ammonium and nitrate as nitrogensources (reference), cultivated with ammonium and nitrate but suppliedwith arginine after the last fertilization event in autumn (arginineloaded) or cultivated with arginine as the sole source of nitrogenthroughout the growth season (arginine cultivated). Chitin is part ofthe fungal cell wall and thus indicates the fraction of mycorrhiza inthe total root system.

FIG. 7 disclose the effect of various proportions of L-Glutamine (Gln)on total biomass production (FIG. 7A) and production of roots (FIG. 7B).

FIG. 8 disclose the effect of L-Asparagine (Asn) on total biomassproduction (FIG. 8A) and production of roots (FIG. 8B).

Through a series of experiments, the inventors have discovered thatplants supplied with a mixture of organic and inorganic nitrogen formswill distribute nitrogen derived from these different forms unevenly sothat a greater share of plant nitrogen derived from organic nitrogenforms are found in roots than in other plant parts. In FIG. 2, resultsfrom an experiment in which small Arabidposis thaliana plants weresupplied either with a mixture of ammonium and nitrate or a mixture ofL-Glutamine and nitrate are shown. FIG. 2 shows that for the wholeplant, c. 50% of nitrogen is derived from uptake of L-Glutamine while c.75% of root nitrogen is derived from this nitrogen form. Conversely, c.45% of whole plant nitrogen is derived from uptake of nitrate while onlyc. 25% of root nitrogen is derived from uptake of this nitrogen form.Similarly, when A. thaliana plants were cultivated on nitrate and onlysmall amounts of L-Arginine was added to the growth media (FIG. 3), ahigher fraction of nitrogen derived from L-Arginine was found in rootscompared to in shoots. These experiments thus show that plants suppliedwith a mixture of nitrogen forms use organic nitrogen primarily for rootgrowth.

To our surprise we also found that root growth of A. thaliana plantssupplied with a mixture of organic and inorganic nitrogen (in this caseL-Glutamine and nitrate) was readily stimulated compared to thatachieved on a mixture of ammonium and nitrate (FIGS. 4A and 4B). In asecond experiment, the effect of different mixtures of nitrogen sourceswas tested on Populus seedlings (FIGS. 5A and 5B). As for A. thaliana, asignificant increase in root mass fraction was found for plants suppliedwith L-Glutamine and nitrate compared to those supplied with ammoniumand nitrate. According to these data, plant growth was similar or betterfor plants supplied with a mixture of organic and inorganic nitrogenforms compared to those given only inorganic forms. At the same time,the root mass fraction was significantly higher for plants supplied witha mixture of organic and inorganic nitrogen. This shows that, at equalor better growth, a higher root mass fraction can be achieved throughcultivating plants on organic nitrogen or mixtures between inorganic andorganic nitrogen compared to when plants are supplied with inorganicnitrogen only.

The current invention relates to the possibility to adjust plant biomassallocation to roots through use of specific amino acids as fertilizersduring plant cultivation. Mixtures in which specific amino acids forms adominant part of the nitrogen in the fertilizers can thus be used tospecifically increase root growth of plants and thus increase the rootmass fraction of the produced plant. Mixtures with a dominance ofinorganic nitrogen forms can, accordingly, be used to specificallyincrease the shoot mass fraction of the plant.

Many plants form symbioses with fungi, called mycorrhiza. It is wellknown that mycorrhizas develop poorly on plants given high amounts ofnutrients (Smith, S. E., and D. J. Read. 1997. Mycorrhizal symbiosis,2^(nd) Edition. Academic Press, New York, N.Y., USA.). Mycorrhizas areknown to be beneficial for plants and promote plant uptake of mineralnutrients and of water as well as to protect plants from variouspathogenes. Thus, cultivation of plants that, under natural conditionsform mycorrhiza, should enable such symbioses to form. As stated above,however, high rates of nutrient addition may severely hamper or may notallow the development of mycorrhiza on cultivated plants.

Several of the fungal species that form mycorrhiza are also known toform edible fruit bodies (mushrooms). However, production of fruitbodieswill also be hampered by high rates of nutrient additions, i.e. theconditions that are used to stimulate plant growth.

The above-mentioned obvious contradiction between efficient cultivationof plants and the simultaneous development of mycorrhiza and of ediblemushrooms is to a significant degree dependent on the addition of largeamounts of nitrogen in the fertilizer.

Furthermore it was very unexpected that the number of root tips and thenumber of fine roots increased to such high levels that it helped theplantlets to survive the first period after plantation.

The examples relates to the use of one amino acid and not two or more.The fertilizer is not intended for invitro use and not for cut flowers.

An ideal fertilizer should hence stimulate not only plant growth butalso growth of symbiotic fungi forming mycorrhiza. Furthermore, an idealfertilizer should also allow for production of fungal fruit bodies. Toour surprise, we found that plants cultivated on amino acids bothdisplayed a high growth rate and vigorous development of mycorrhiza. Thestimulation of mycorrhiza formation was found both on plants raised onamino acids and on plants raised on inorganic nitrogen sources (ammoniumplus nitrate) but later supplied with amino acids.

The fertilizer may contain at least 5% (wt), at least 10% (wt), at least15% (wt), at least 20% (wt), at least 25% (wt), at least 30% (wt), atleast 35% (wt), at least 40% (wt), at least 45% (wt), at least 50% (wt),at least 55% (wt), at least 60% (wt), at least 65% (wt), at least 70%(wt), at least 75% (wt), at least 80% (wt), at least 85% (wt), at least90% (wt), or at least 95% (wt), of the nitrogen source therein, is anL-amino acid, preferably L-arginine and/or L-glutamine.

Experimental Procedures Example 1 Allocation of Arginine-Nitrogen inArabidopsis

The experiment was performed with wild type Arabidopsis on sterile agarplates containing half strength Murashige and Skoog (MS) medium(Murashige and Skoog, 1962), with 0.65% w/v agar (plant agar, DuchefaBiochemie), 0.5% w/v sucrose amended with 3 mM nitrate and 30 μM U-¹⁵N(>98% ¹⁵N) L-Arg and buffered to pH 5.8 with 3.6 mM MES(2N-morpholinoethanesulfonic acid). Plants were grown for 19 days when20 plants were harvested and divided into 4 replicates (i.e. eachreplicated consisted of 5 plants). Shoots and roots were separated;roots were rinsed and cleaned thoroughly three times in a solution of0.5 mM CaCl₂ to remove adhered compounds from surfaces. Shoots and rootswere dried at 60° C. overnight, weighed and homogenized. Finally,samples were analyzed using a Europe Scientific Isotope Ratio MassSpectrometer to determine total N and ¹⁵N contents. The results aredisclosed in FIG. 3.

Example 2 Allocation of Biomass and Glutamine-N in Arabidopsis andPoplar

Allocation experiments were performed with wild type Arabidopsis onsterile agar plates and in the case of poplar, in plastic boxes,containing the equivalent of nitrogen-free, half strength Murashige andSkoog (MS) medium (Murashige and Skoog, 1962), with 0.8% w/v agar (plantagar, Duchefa Biochemie), 0.5% w/v sucrose and pH was set to 5.8 usingMES buffer. Nitrogen was added to the agar either as an equimolarmixture of NH₄ ⁺ and NO3⁻ or as an equimolar mixture, corresponding to50% of each of L-Gln and NO3⁻, both mixtures at a total ratecorresponding to 3 mM N. Four labelling treatments were carried out,i.e. two for each N mixture. Thus half of the plates with the NH4NO3mixture contained labelled NH₄ ⁺, the other half contained labelledNO3⁻. Similarly, half of the plates with L-Gln:NO3⁻ mixtures containedlabelled L-Gln, the other half contained labelled NO3−. For eachlabelling treatment, 1% of the N source was administered as ¹⁵N. Sterilefiltered L-Gln was added to the agar mixture after autoclaving.Arabidopsis plants were harvested after 21 days and poplar plants after28 days of growth. Shoots and roots were dried at 60° C. overnight,weighed and homogenized. Finally, samples were analyzed using a EuropeScientific Isotope Ratio Mass Spectrometer to determine total N and ¹⁵Ncontents. The amount of N derived from either of the two N sources indifferent plant parts (i.e. shoots and roots) were calculated fromvalues of excess atom % 15N and total N content of the respective plantpart. Root fractions of plants from the two different N mixtures werecalculated as the percentage of total plant biomass present in roots.The results regarding Arabidopsis are disclosed in FIG. 4 and theresults regarding Populus is disclosed in FIG. 5.

TABLE 1 The root mass fraction, i.e. the fraction of whole-plant biomasspresent in roots, of Arabidopsis thaliana and Populus deltoides plantsgrown on either a mixture of NH4+ and NO3− or a mixture of NO3− andL-Gln Species NH4+ NO3− mixture NO3− L-Gln mixture Arabidopsis 14.1 ±0.6% 19.2 ± 0.3% Populus 20.2 ± 0.4% 26.2 ± 1.7%

Example 3 Evaluation of Mycorrhiza of Scots Pine Roots

Plants were cultivated outdoors during one growth season in northernSweden. Plants were supplied with a complex nutrient solution witheither ammonium nitrate or arginine as nitrogen sources.Arginine-cultivated seedlings were fertilized once a week during thegrowth season (in total 50 mg N per seedling) while reference plantswere fertilized 2-3 times a week (in total 71,5 mg N per seedling).Arginine-loaded seedlings received the same treatment as the referencewith the exception that they also received a pulse of arginine after thelast fertilization event in early autumn. The amount of argininesupplied in this pulse corresponded to 5 mg nitrogen per seedling. Theaverage chitin content of the roots can be found in FIG. 6 and in Table2. The values are shown as average value±standard evaluation, n=6.

TABLE 2 Chitin content of Scots pine roots Chitin content (mg chitin/groot) Fertilizer Average values ± SE, n = 6 Reference 1.35 ± 0.39Arginine loading 3.90 ± 1.05 Arginine cultivation 2.72 ± 1.81

The results clearly show that fertilization with arginine results insubstantially higher content of chitin in roots which indicatesmycorrhiza formation.

Example 4 Typical Fertilization Compositions

Composition A:

Component Amount L-Arginine 233140 g HCl (37% aqueous solution) 138990 gBenzoate (preservative) 1000 ppm Water 700000 g Physical data: ξ 1.08 pH3.20 Total weight (kg) 1080 Total volume (l) 1000

Arginine and the preservative was added to and dissolved in water andsubsequently, the pH was adjusted by titrating with concentrated HCl.The final pH was determined before diluting with water up to the finalvolume of 1000 I.

Composition B:

Component Amount MgSO₄•7 H₂O 40900 g K₂SO₄ 27270 g KH₂PO₄ 54530 g KCl40900 g Arginine 233140 g Micro+ 55820 g HCl (37% aqueous solution)147560 g Benzoate (preservative) 1000 ppm Water 640000 g Physical data ξ1.20 pH 3.20 Total weight (kg) 1200 Total volume (l) 1000

The salts and the preservative were first dissolved in water and thenMicro+(trace element composition available from LMI AB, Sweden) wasadded. Subsequently, arginine was dissolved and pH was adjusted to 3.2with aqueous HCl (37%). Finally, water was added up to 1000 I.

Example 5 Growth and Allocation of Biomass as Affected by Nitrogen Formin Arabidopsis

Arabidposis (Arabidposis thaliana) plants were grown in sterile culturefor 21 days on media amended with different nitrogen sources. All mediahad a total nitrogen concentration of 6 mM and all other macro and micronutrients supplied in the same amounts in each treatment.

From the experiment with the L-amino acid L-glutamine it can be seenthat there is clear and unexpected correlation between the root biomassand the amount of L-glutamine added as the nitrogen source, FIG. 7A, 7Band Table 3. Furthermore, it can be seen that the root fraction (FIG.7B) is higher when a L-amino acid is added compared to when onlyinorganic nitrogen is added. This is very clear when the L-amino acidL-asparagine is added as seen in FIG. 8B and Table 4.

It could be noted that in spite of the total biomass is equal with thedifferent nitrogen sources as seen in FIGS. 7A and 8A, the root fractionis higher then expected, as seen in FIGS. 7B and 8B.

TABLE 3 Root fraction and total biomass with L-glutamine Root Total Nsource fraction std stderr biomass std stderr NH4NO3 0.12 0.02 0.01 6.141.12 0.42 NO3 0.12 0.01 0.01 4.63 0.98 0.35 33% Gln 67% NO3 0.15 0.010.00 6.59 0.99 0.35 50% Gln 50% NO3 0.16 0.01 0.00 6.16 1.06 0.37 67%Gln 33% NO3 0.17 0.01 0.00 6.13 1.37 0.52

TABLE 4 Root fraction and total biomass with L-asparagine Root Total Nsource fraction std stderr biomass std stderr NH4NO3 0.12 0.02 0.01 6.141.12 0.42 NO3 0.12 0.01 0.01 4.63 0.98 0.35 33% Asn 67% 0.17 0.01 0.006.23 0.76 0.27 NO3

1. Use of a fertilizer characterized in that it comprises a naturallyoccurring L-amino acid as a nitrogen source for stimulating root growth.2. Use of a fertilizer characterized in that it comprises a naturallyoccurring L-amino acid as a nitrogen source for stimulating mycorrhizadevelopment.
 3. Use of a fertilizer according to claim 1, characterizedin that the naturally occurring L-amino acid is chosen from the group ofL-arginine L-asparagine, and L-glutamine as a nitrogen source, forstimulating root growth and/or for stimulating mycorrhiza development.4. Use of a fertilizer according to claim 1, characterized in that thefertiliser also comprises an inorganic nitrogen compound such as nitrateor ammonium.
 5. Use of a fertilizer according to claim 1, characterizedin that at least 30% (wt) of the nitrogen source therein, preferably atleast 70% (wt) of the nitrogen source therein, preferably at least 85%(wt), and most preferably at least 90% (wt), is a L-amino acid and theother nitrogen source is an inorganic nitrogen comprising compound, suchthat the stimulation of the root and shoot growth is related to theratio between the L-amino acid and the inorganic nitrogen comprisingcompound.
 6. Use of a fertilizer according to claim 1, characterized inthat the L-amino acid is chosen from the group of L-arginine,L-asparagine, glycine, L-glutamic acid and L-glutamine.
 7. Use of afertilizer comprising a naturally occurring L-amino acid, according toclaim 1, characterized in that the fertilizer also contains a suitablepreservative.
 8. Use of a fertilizer comprising a naturally occurringL-amino acid, according to claim 1, characterized in that thepreservative is selected from the group of a benzoate such as potassiumbenzoate, acetic acid, salicylic acid, propionic acid, sorbic acid,citric acid, and alexin plus.
 9. Use of a fertilizer comprising anaturally occurring L-amino acid, according to claim 1, characterized inthat the fertilizer is solid.
 10. Use of a fertilizer comprising anaturally occurring L-amino acid, according to claim 1, characterized inthat the fertilizer is a solution.